The process of embryonic bone formation involves the creation of an extracellular matrix that mineralizes during the course of tissue maturation. This matrix is subject to constant remodeling during the lifetime of an individual, through the combined actions of osteoblasts and osteoclasts. A careful balance of matrix formation and resorption must be maintained because perturbations can result in various bone disorders.
The extracellular matrix of bone consists of two phases, an organic phase and a mineral phase. The organic phase consists primarily of the collagen type I fibrils that are associated with a number of noncollagenous matrix proteins. Interest in the noncollagenous proteins of the bone has been greatly stimulated since Urist first demonstrated that demineralized bone extracts could induce ectopic bone formation (Urist, M. R., Science, 150:893–899 (1965)). Noncollagenous proteins of bone are now believed to be involved in mineralization as well as the local regulation of bone cell function (Heinegard, D. and Oldberg, A., Connective Tissue and Its Heritable Disorders (Royce, P. M. and Steinmann, B., EDS), pages 189–209, Wiley-Liss, New York (1993), and Von der Mark, K. and Goodman, S., id.). In the past few years, a number of noncollagenous proteins of bone have been isolated and characterized; among these are osteocalcin, osteopontin, osteonectin and bone sialoprotein (Heinegard, D. and Oldberg, A., FASEB J., 3:2042–2051 (1985)).
A clonal osteogenic cell line (MN7) from bone marrow stroma of the adult mouse has been established (Mathieu, E., et al., Calcif. Tissue Int., 50:362–371 (1992)). These cells, under appropriate conditions, undergo typical osteoblastic differentiation in vitro and are able to form a mineralized extracellular matrix (Mathieu, E. and Merregaert, J., J. Bone Miner. Res., 9:183–192 (1994)).
A cDNA coding for a novel secretory protein of mouse (p85), has been cloned, characterized and genetically mapped (Bhalerao, J., et al., J. Biol. Chem., 270 (27): 16385–16394 (1995)). The full-length cDNA contains an open reading frame of 1677 bp encoding a protein of 559 amino acids. The clone contains a hydrophobic signal peptide characteristic of a secreted protein. The message of 1.9 kb is expressed in various tissues, such as liver, heart, lungs, etc., whereas a splice variant was present in embryonic cartilage in skin. This gene p85, called Ecm1 for extracellular matrix protein 1, maps on chromosome 3 of mouse in a region containing several loci involved in skin development disorders.
The polypeptide of the present invention has highest amino acid sequence homology to growth factor Ecm1.